CA 19-9 is a secreted protein that is implicated in various cancers. It is overexpressed in salivary gland mucoepidermoid carcinomas and gastric, pancreatic, and colonic (gastrointestinal) adenocarcinomas, but is not expressed in breast, kidney, and prostate carcinomas. CA 19-9 staining is also implicated in Mirizzi's Syndrome or other bile duct and liver diseases.